[x86] Fix AVX maskload/store intrinsic prototypes.

The mask value type for maskload/maskstore GCC builtins is never a vector of
packed floats/doubles.

This patch fixes the following issues:
1. The mask argument for builtin_ia32_maskloadpd and builtin_ia32_maskstorepd
   should be of type llvm_v2i64_ty and not llvm_v2f64_ty.
2. The mask argument for builtin_ia32_maskloadpd256 and
   builtin_ia32_maskstorepd256 should be of type llvm_v4i64_ty and not
   llvm_v4f64_ty.
3. The mask argument for builtin_ia32_maskloadps and builtin_ia32_maskstoreps
   should be of type llvm_v4i32_ty and not llvm_v4f32_ty.
4. The mask argument for builtin_ia32_maskloadps256 and
   builtin_ia32_maskstoreps256 should be of type llvm_v8i32_ty and not
   llvm_v8f32_ty.

Differential Revision: http://reviews.llvm.org/D13776

llvm-svn: 250817